The size and scale of our universe is nearly incomprehensible. While many comparisons have been formulated to describe certain cosmological distance (such as from the Earth to the Moon, and so on), I believe that only one can even claim to do justice to the size of the universe. To gain even a slight comprehension of our universe’s scale, we should examine the amount of time it take light to travel its “diameter.” Light is the fastest “thing” in the universe, usually. We know this from not only our experimental and practical observations, but also from our theoretical models. Einstein’s Theory of Special Relativity tells us that nothing can surpass the speed at which light travels through a vacuum.
With this said, our universe is estimated to be approximately 13.8 billion years old, which means that can observe light from up to 13.8 light-years away. This means that our observable universe is about 27.6 billion light-years in diameter. Light, which we understand to travel about 671 million miles per hour, cannot travel the hypothetical “end-to-end” distance of the observable universe, which is thought to be approximately 93 BILLION light-years. How is this possible? If light is the fastest type of matter/energy in our universe, then how could the radius (in light-years) be over three times the age of the universe? The answer is that the very fabric of the universe, spacetime, is expanding faster than light can travel and in all directions. (The fabric of the universe is not bound by the limitations of lightspeed, which is an upper limit on objects moving through space, but not space itself.) If the universe continues to expand at this rate, light will never travel the universe from end to end. There really is not way of doing justice to the universe’s incomprehensible massiveness. There is nothing to compare our rapidly expanding universe to.
